Uracil, U, undergoes amide-iminol tautomeric shifts because of its resonance structures resulting from the N and O substitutents. Also because any nuclear instability the molecule may have from the lack of formal aromaticity is compensated by the cyclic-amidic stability.[2] The keto tautomer is referred to the lactam structure, while the enol tautomer is referred to as the lactim structure. These tautomeric forms are predominant at pH=7. The lactam structure is the most common form of uracil.

Oxidative degradation of uracil produces urea and maleic acid in the presence of H2O2 and Fe2+ or in the presence of diatomic oxygen and Fe2+.

Uracil is a weak acid, the first site of ionization of uracil is not known.[5] The negative charge is placed on the oxygen anion and produces a pKa of less than or equal to 12. The basic pKa = -3.4, while the acidic pKa = 9.389. In the gas phase, uracil has 4 sites that are more acidic than water.[6]

Reactions

Uracil readily undergoes regular reactions including oxidation, nitration, and alkylation. While in the presence of PhOH/NaOCl, uracil can be visualized in the blue region of UV light.[2] Uracil also has the capability to react with elemental halogens because of the presence of more than one strongly electron donating group.[2]

When uracil reactes with anhydrous hydrazine a first order kinetic reaction occurs and the ring of uracil opens up.[8] If the pH of the reaction increases to >10.5 the uracil anion forms making the reaction go much slower, the same slowing of the reaction occurs if the pH decreases because of the protonation of the hydrazine.[8] The reactivity of uracil is unchanged even if the temperature changes.[8]

Uses

Uracil can be used for drug delivery and as a pharmaceutical. When elemental fluorine is reacted with uracil, 5-fluorouracil is produced. 5-Fluorouracil is an anticancer drug (antimetabolite) used to masquerade as uracil during the nucleic acid replication process.[1] The drug molecule also fools the enzymes that help in this process to incorporate this compound in the replication and not uracil, this causes the biological polymer (cancer) not to continue synthesizing.[1]

↑ 12.012.1Pozharskii, A.F.; et al.Heterocycles in Life and Society: An Introduction to Heterocyclic Chemistry and Biochemistry and the Role of Heterocycles in Science, Technology, Medicine, and Agriculture. New York: John Wiley and Sons, 1997.